1. Field of the Invention
The present invention relates to a lenticular lens sheet for use in a rear projection screen that allows light emitted from an image source, incident on the rear of the screen, to emerge toward the viewer's side, and more particularly to a lenticular lens sheet capable of reducing the color shift.
2. Description of Related Art A method in which imaging light emitted from three CRT's (projection tubes) for R, G and B, serving as an image source, are magnified by projection lenses and are projected on a rear projection screen (hereinafter sometimes abbreviated to a “screen”) is known as a method of displaying an image on a large-sized screen.
Specifically, for example, in such a rear projection display 10 as is shown in FIG. 1, imaging light emitted from three CRT's 1 for R, G and B, serving as an image source, are magnified by respective projection lenses 2 and are projected on the plane of a rear projection screen 5. The rear projection screen 5 comprises a Fresnel lens sheet 3 and a lenticular lens sheet 4 and allows the imaging light emitted from the CRT's 1, incident on the rear of the screen, to emerge toward the viewer's side at the desired angle of view.
For such a rear projection screen 5, the CRT's 1 for R, G and B are usually so arranged that the CRT 1 for green color (G) is positioned directly in front of the screen and that the CRT 1 for red color (R) and the CRT 1 for blue color (B) are positioned on either side of the CRT 1 for G. Therefore, of the imaging light incident on the front surface of the screen, red light (R) and blue light (B) are, relative to green light (G), to enter the screen at an angle of convergence θ with the normal to the screen. Owing to this angle of convergence θ at which red light (R) and blue light (B) converge on the screen, either R or B color appears stronger as the point from which the image projected on the rear projection screen 5 is viewed is changed horizontally, and the marginal parts of the screen get colored. This phenomenon is called “color shift,” and it is hoped that the color shift will be reduced.
Studies have already been made on this phenomenon, and Japanese Laid-Open Patent Publication No. 59436/1983, for example, proposes a technique in which the eccentricities of the elliptical planes of lens elements to be formed on both surfaces of a lenticular lens sheet are selected so that they are nearly equal to the reciprocal of the refractive index of a material from which the lens elements are made. Further, Japanese Laid-Open Patent Publications No. 280729/1987, No. 190835/1990 and No. 150371/1993 propose techniques in which the shapes of lens elements to be formed on both surfaces of a lenticular lens sheet are numerically specified.
The above-described color shift is observed more clearly as the angle θ at which imaging light converges increases. In line with the recent trend toward thinner televisions, the angle of convergence θ tends to become greater than ever before. For this reason, it has been getting difficult to reduce the color shift by the color-shift-reducing techniques proposed so far in the above-described patent publications, etc., and the situation has been changing to that these conventional techniques cannot always satisfactorily fulfill the demand for color-shift reduction.